Enable multiple tabs close warning in Firefox

When you have multiple tabs open in a Firefox window and you try to close the main Firefox window, then Firefox gives a warning asking you if you would like to save all the open tabs for next time Firefox starts? The warning looks like the picture shown below :

If you felt annoyed by this and checked the checkbox labeled Do not ask next time, then Firefox will not show the warning anymore. What if you want this warning back? Do not worry, you can easily enable this warning which is shown everytome you close a Firefox window with multiple open tabs. Here is how :

Start Mozilla Firefox.

Type about:config in the location bar and press Enter.

Firefox will show a warning. Click on the button labeled I’ll be careful I promise! to proceed.

In the Filter field type tabs.warn. You would see a preference named tabs.warnOnClose as shown.

Double click on tabs.warnOnClose to change its value to true. The true value means that the Firefox will ask show you a warning when you try to close a Firefox window with multiple tabs open.

After changing the value, restart the browser for the changes to take effect.